Tohatsu 90 Prop Stike Issues

[Scots-Andy]

I have a 90hp direct injection 2008 model tohatsu 2 stroke. I am currently operating it from the back of a large zodiac based in northern Canada. I struck a rock with the tips of the propellor blades, this took a ?cm gouge out of the blade-tip from two (of three) blades. Unfortunately the stress propogation also caused severe damage to my drive chain and lower casing.

The entire lower casing cracked open around the drive chain bulge, instantly draining all the oil and exposing the gears. Not only the casing but also the drive chain itself suffered damage - the area where the horizontal driveshaft mounts into the aluminum casing, behind where the gears mesh with the gears for the verical shaft, has numerous cracked parts and broken pieces. The gears themselves are absolutely fine, no missing teeth, anything. When I removed the propellor and the top locking bolt the entire bottom of the motor, from the drivechain down simply fell off into my hand along the crack. The strike occured as the motor was barely engaged in forward gear, the boat was travelling at approximately 4 knots (we had just left harbour). Only the tips of the propellor hit, the leg, the lower casing and the skeg don`t even have a scratch. The drive chain seems to have exploded through the aluminum lower casing - clearly seen by the outward bending metal.

I have never seen or heard of such severe damage to a motor from a minor prop strike. Until this engine purchase i have never used a tohatsu. I was lead to believe that a whole load of safety features are built into the motor to stop gear and drive chain damage from prop strikes.

The engine requires an entire lower leg replacement. has anyone heard of any aluminum case defects on Tohatsu lower leg units? Or has knowledge of the safety systems installed on the engine designed to prevent this from happening?

The engine had been used for 10 hours prior to this happening, all oil and fluids were full and everything was working fine.

Any help would be appreciated!

Cheers

 

[JB]

Re: Tohatsu 90 Prop Stike Issues

Wow!! Never saw or heard of that much damage from a prop strike.

I wonder if there was a defect in manufacture that was triggered to blow up by what should have been a minor event.

"drive chain". Are you referring to what I always have called the "drive train"?

I think I would get a Tohatsu rep. to take a look at the remains and see if it might be covered by warranty.

 

[TOHATSU GURU]

Re: Tohatsu 90 Prop Stike Issues

Simply not possible as described.

 

[Scots-Andy]

Re: Tohatsu 90 Prop Stike Issues

JB,
Thanks for the assistance, my engine is a 2007, not a 2008 - i checked it again today! I do indeed mean the drive-train not drive-chain, my apologies for the mixup. I`m going to call my Tohatsu dealer in Montreal, however, i`m in the Northern Canada just now, the boat was a new workboat, so shipping parts or a new engine is incredibly expensive. But, i really don`t see an alternative. I will look at the warranty.

However, posts like:

Simply not possible as described.

Are both condescending and unhelpful. I accurately described exactly what i think happened to the motor and boat - i should know - i was driving the thing. I am not a mechanic or outboard engineer, however i have been on the sea many many years so I speculated as to the cause of the problem - suggesting it was stress propogation up the drive chain/train from the hit on the propellor blades. If this isn`t possible can you explain why? Or alternatively suggest how this happened? I have no idea if this is a common problem with Tohatsu engines?

May be a daft question but, would i be able to replace the Tohatsu lower leg (or parts of it) with another leg from a different outboard motor, e.g. we have a Yamaha 90 in the workshop who`s engine is blown but everything else if fine. Or are the parts not interchangable in any way - i`d imagine not, but i thought i`d check!

If you would like to see the pictures of the blown side casing and mangled end-piece of the lower drive-train, i can probably supply them - but i have no idea how to upload them.

Your time and comments are valued greatly, thanks.

 

[TOHATSU GURU]

Re: Tohatsu 90 Prop Stike Issues

Good luck.

 

[lots of boats]

Re: Tohatsu 90 Prop Stike Issues

Hi

Yep, not only possible, but I have a whole pile of broken Tohatsu 90 TLDI
gear cases. We frequently tig weld the cavitation plates back on, because they break easily when a floating stick gets caught in the prop and comes around the port side and breaks off the plate. The interesting thing is that we have welded skegs, and other parts on other brands of motors too, but the aluminum in the Tohatsu's is the hardest to weld because of the porosity and contamination in it. Welding it requires two and usually three complete welding cycles. You have to weld it hot, clean it out with a rotary file, not a grinder, weld it hot again, and then clean it out again and usually weld it a third time. Paint usually isn't an issue because the paint isn't very well stuck. The other thing Tohatsu lower ends will do is the bolts will strip out easily. The two ears that hold the bearing carrier into the gear case tend to break off too. But to get to your question, I had one new gear case come with no needle bearing at the back of the prop shaft where it sits inside the forward gear. So in neutral the whole thing shook and rattled, (even louder than the air pump and the intake noise, if that is possible) but when it was put into gear the clutch dog and consequently the prop shaft was supported by the bearings on the outside of the gears. It worked for a while before that one came apart. My guess on what happened to your gear case is that the housing broke about even with the place where the pinion gear meshes with the forward and reverse gear. Remember, all the gears mesh all the time, the clutch dog is moved back and forth to determine which way the prop shaft will turn, but if the prop shaft was not properly supported, either because of a missing bearing, or from improper shimming of the gears, and it stopped from a prop strike, it could move sideways inside the housing, and given the pot metal these cases are made from, the rotating gear would chew the whole case apart. Sound about right? Cheers.

 

[TOHATSU GURU]

Re: Tohatsu 90 Prop Stike Issues

When you run into something and it causes damage that is called an accident, not a defect. Insurance pays for accidents. Engine manufacturers do not.

 

[lots of boats]

Re: Tohatsu 90 Prop Stike Issues

Hi Scots Andy

Let me know whether you have found the defect in the 90TLDI that allowed the minor prop strike to cause so much damage.

It may help if you look at a parts manual and familiarize yourself with the way gear cases are assembled. I pointed out one way that can allow a propshaft to wobble, in neutral, i.e not putting the bearings on the front of the shaft. You can also look at the bearing carrier to see whether it was held in properly, if the bearing carrier isn't secure, the whole prop shaft can move forward and back, and this can allow the reverse gear to come away from the pinion gear. Don't assume that because this was a new motor it was assembled correctly. If you are going to run these motors you have to figure out how to work on them.

Two of the many things you are going to have problems with in the 90TLDI in Northern Canada are cold weather and bent prop shafts. Below -5 degrees C, you can forget using this motor. You can repair your own props and prop shafts if you want to learn how. Cheers.

 

[TOHATSU GURU]

Re: Tohatsu 90 Prop Stike Issues

Cheesey malice

 

[chevyjet]

Re: Tohatsu 90 Prop Stike Issues

I don`t think that is cheesy at all it sounds about right, these moters tend to be lighter duty and if there is truly no marks on the skeg and just the tips of the prop hit at idle then there was some other problem.

 

[lots of boats]

Re: Tohatsu 90 Prop Stike Issues

Thanks Chevyjet,

I see you are another nooby? Me too, and they didn't like me.

Cheers.

 

[JB]

Re: Tohatsu 90 Prop Stike Issues

Our problem here, LOB, is that we get a your strongly negative view of engines that, worldwide, are probably the most used and most trusted brand out there.

Without other views we are at risk of getting a distorted picture.

We only have Andy's testimony about his damage. I don't contradict his version, but I know how perceptions can differ from reality.

So far you have attacked Tohatsu TLDI 90s on about four issues, in each case deciding that the experience you describe is indicative of poor quality throughout.

You obviously have a lot of TLDI 90s and a lot of experience with them. We appreciate the benefits of your experience but think you would get a better hearing if you would lighten up on the judgement.

 

[TOHATSU GURU]

Re: Tohatsu 90 Prop Stike Issues

"My choices are to slam Tohatsu, or to say, well, I may be the worst case scenario for that company, but they should learn from this. The first thing they haven't figured out is that the internet has changed the way that big corporations deal with customers, there are no secrets."

Edited for more peaceful discussion. JB